1. Field of the Invention
The present invention relates to an apparatus and method for assisting image diagnosis using a three-dimensional medical image representing a subject's internal structure constituted by branch and peripheral structures, such as a lung. The invention also relates to a computer readable recording medium on which is recorded a program for the same.
2. Description of the Related Art
As a technology for assisting image diagnosis using a three-dimensional medical image representing a chest obtained by a CT device, a technology that automatically detects an abnormal opacity, such as lung cancer and the like, from the three-dimensional medical image is known.
For example, a method of detecting lung cancer opacity from a three-dimensional CT image representing a chest using a two-dimensional N-Quoit filter, a variable neighborhood type Laplacian filter, a Min-DD filter, and a contrast filter, each extended to three-dimensions, is known as described, for example, in a literature “Performance Evaluation of 3-D Enhancement Filters for Detection of Lung Cancer from 3-D Chest X-ray CT Images”, by A. Shimizu et al., Medical Imaging Technology, Vol. 13, No. 6, pp. 853-864, November 1995 (Non-patent Document 1).
Further, a method of automatically classifying nodular opacities into solid nodules and ground glass opacities is proposed as described, for example, in a literature “Automatic classification method of Solid and Ground Glass Opacity in Chest X-ray CT Images” by T. Tomida et al., IEICE Technical Report, MI2001-150 (2010-01), Vol. 109, No. 407, pp. 397-400, January 2010 (Non-patent Document 2). The method achieves the automatic classification by dividing a detected pulmonary nodular opacity into a nucleus and a periphery through gray value threshold processing or contrast evaluation, obtaining the ratio of the nucleus in the opacity as a characteristic amount, in addition to characteristic amounts with respect to the volume, sphericity, horizontal to vertical ratio, average gray value, and the like, and performing a canonical discriminant analysis.
As for a method of detecting a lesion area other than lung cancer, a method that detects an area of lung fields where pixel values are less than a predetermined threshold value (threshold value of −960 HU for a non-contrast enhanced CT image) as an emphysema area is known, as described for example, in a literature “Quantitation of emphysema by computed tomography using a “density mask” program and correlation with pulmonary function tests” by M. Kinsella et al., Chest, 97, pp. 315-321, 1990 (Non-patent Document 3).
Further, a method in which lung parenchymal tissue in a CT image of lungs is segmented, then a perfusion map of the segmented image is generated, and an abnormally underperfused area is detected is known as described, for example, in U.S. Pat. No. 7,715,608 (Patent-document 1).
In an actual medical site, when a detection result for lesion from an image and other examination results are comprehensively evaluated and a definitive diagnosis is established that the lesion is a certain disease, the lesion is resected, removed, or cauterized. Here, in order to preserve, as much as possible, the function of the organ in which the lesion is found after the treatment, the treatment target area should be limited as small as possible. On the other hand, if the target area is not large enough, a portion of the lesion may remain and a metastasis may possibly occur. Thus, it is necessary to appropriately determine the treatment target area before treating the affected area.
The method described in each of Non-patent Documents, however, only detects an abnormal area in lung fields and the documents do not describe at all how to assist in determining the treatment target area when a certain treatment needs to be performed on the abnormal area.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide an apparatus and method capable of identifying a necessary and sufficient treatment target area for an abnormal area when an image diagnosis is performed using a three-dimensional medical image representing an inner structure of a subject constituted by branch and peripheral structures. It is a further object of the present invention to provide a computer readable recording medium on which is recorded a program for the same.